Method of making sacrificial coating for an intermediate transfer member of indirect printing apparatus

ABSTRACT

A method of making a sacrificial coating composition is disclosed. The method comprises emulsifying an oil with surfactant and water to form an oil-in-water emulsion; and combining ingredients comprising (i) at least one polymer, (ii) at least one hygroscopic material, (iii) the oil-in water emulsion and (iv) water to produce the sacrificial coating composition. The at least one polymer is selected from the group consisting of a hydrophilic polymer, a latex comprising polymer particles dispersed in a continuous liquid phase, or mixtures thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of, and claims priority to,U.S. patent application Ser. No. 14/493,569, filed on Sep. 23, 2014 (nowallowed) the disclosure of which is hereby incorporated herein byreference in its entirety.

DETAILED DESCRIPTION Field of the Disclosure

This disclosure relates generally to a method of making a sacrificialcoating for use on an intermediate transfer member of an inkjet printer.

Background

In aqueous ink indirect printing, an aqueous ink is jetted on to anintermediate imaging surface (sometimes referred to herein as anintermediate transfer member), which can be, for example, in the form ofa blanket. The ink is partially dried on the blanket prior totransfixing the image to a media substrate, such as a sheet of paper. Toensure excellent print quality it is desirable that the ink drops jettedonto the blanket spread and become well-coalesced prior to drying.Otherwise, the ink images appear grainy and have deletions. Lack ofspreading can also cause missing or failed inkjets in the printheads toproduce streaks in the ink image. Spreading of aqueous ink isfacilitated by materials having a high energy surface.

In order to facilitate transfer of the ink image from the blanket to themedia substrate after the ink is dried on the intermediate imagingsurface, a blanket having a surface with a relatively low surface energyis preferred. Rather than providing the desired spreading of ink, lowsurface energy materials tend to promote “beading” of individual inkdrops on the image receiving surface.

Thus, an optimum blanket for an indirect image transfer process musttackle both the challenges of wet image quality, including desiredspreading and coalescing of the wet ink; and the image transfer of thedried ink. The first challenge, wet image quality, prefers a highsurface energy blanket that causes the aqueous ink to spread and wet thesurface. The second challenge, image transfer, prefers a low surfaceenergy blanket so that the ink, once partially dried, has minimalattraction to the blanket surface and can be transferred to the mediasubstrate.

Various approaches have been investigated to provide a solution thatbalances the above challenges. These approaches include blanket materialselection, ink design and auxiliary fluid methods. With respect tomaterial selection, materials that are known to provide optimum releaseproperties include the classes of silicone, fluorosilicone, afluoropolymer, such as TEFLON or VITON, and certain hybrid materials.These materials have low surface energy, but provide poor wetting.Alternatively, polyurethane and polyimide have been used to improvewetting, but at the cost of ink release properties. Tuning inkcompositions to address these challenges has proven to be very difficultsince the primary performance attribute of the ink is the performance inthe print head. For instance, if the ink surface tension is too high itwill not jet properly and it if is too low it will drool out of the faceplate of the print head.

Identifying and developing new techniques and/or materials that improvewet image quality and/or image transfer would be considered a welcomeadvance in the art.

SUMMARY

An embodiment of the present disclosure is directed to a method ofmaking a sacrificial coating composition. The method comprisesemulsifying an oil with surfactant and water to form an oil-in-wateremulsion; and combining ingredients comprising (i) at least one polymer,(ii) at least one hygroscopic material, (iii) the oil-in water emulsionand (iv) water to produce the sacrificial coating composition. The atleast one polymer is selected from the group consisting of a hydrophilicpolymer, a latex comprising polymer particles dispersed in a continuousliquid phase, or mixtures thereof.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the present teachings, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the presentteachings and together with the description, serve to explain theprinciples of the present teachings.

FIG. 1 is a flow charge of a method of making a sacrificial coatingcomposition, according to an embodiment of the present disclosure.

FIG. 2 shows optical microscope images taken of sacrificial coatings, asdescribed in the examples below.

FIG. 3 shows images of ink transfer test results, as discussed in theexamples below.

FIGS. 4, 5 and 6 show optical microscope images taken of sacrificialcoatings, as described in the examples below

FIGS. 7 and 8 shows images of ink transfer test results, as discussed inthe examples below.

It should be noted that some details of the figure have been simplifiedand are drawn to facilitate understanding of the embodiments rather thanto maintain strict structural accuracy, detail, and scale.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to embodiments of the presentteachings, examples of which are illustrated in the accompanyingdrawings. In the drawings, like reference numerals have been usedthroughout to designate identical elements. In the followingdescription, reference is made to the accompanying drawings that form apart thereof, and in which is shown by way of illustration a specificexemplary embodiment in which the present teachings may be practiced.The following description is, therefore, merely exemplary.

As used herein, the terms “printer,” “printing device,” or “imagingdevice” generally refer to a device that produces an image on printmedia with aqueous ink and may encompass any such apparatus, such as adigital copier, bookmaking machine, facsimile machine, multi-functionmachine, or the like, which generates printed images for any purpose.Image data generally include information in electronic form which arerendered and used to operate the inkjet ejectors to form an ink image onthe print media. These data can include text, graphics, pictures, andthe like. The operation of producing images with colorants on printmedia, for example, graphics, text, photographs, and the like, isgenerally referred to herein as printing or marking. Aqueous inkjetprinters use inks that have a high percentage of water relative to theamount of colorant and/or liquid vehicle in the ink.

The term “printhead” as used herein refers to a component in the printerthat is configured with inkjet ejectors to eject ink drops onto an imagereceiving surface. A typical printhead includes a plurality of inkjetejectors that eject ink drops of one or more ink colors onto the imagereceiving surface in response to firing signals that operate actuatorsin the inkjet ejectors. The inkjets are arranged in an array of one ormore rows and columns. In some embodiments, the inkjets are arranged instaggered diagonal rows across a face of the printhead. Various printerembodiments include one or more printheads that form ink images on animage receiving surface. Some printer embodiments include a plurality ofprintheads arranged in a print zone. An image receiving surface, such asan intermediate imaging surface, moves past the printheads in a processdirection through the print zone. The inkjets in the printheads ejectink drops in rows in a cross-process direction, which is perpendicularto the process direction across the image receiving surface.

As used in this document, the term “aqueous ink” includes liquid inks inwhich colorant is in a solution, suspension or dispersion with a liquidvehicle that includes water and/or one or more liquid vehicles. The term“liquid vehicle” is defined herein to include both liquid solvents thatmay dissolve a solute into a solution and liquid carriers that holdparticles in a suspension or dispersion without dissolving the particle.

As used herein, the term “hydrophilic” refers to any composition orcompound that attracts water molecules or other solvents or liquidcarriers used in aqueous ink. As used herein, a reference to ahydrophilic composition refers to a liquid vehicle that carries ahydrophilic agent. Examples of liquid vehicles include, but are notlimited to a liquid, such as water or alcohol, that carries adispersion, suspension, or solution.

As used herein, a reference to a dried layer or dried coating refers toan arrangement of a hydrophilic compound after all or a substantialportion of the liquid vehicle has been removed from the compositionthrough a drying process. As described in more detail below, an indirectinkjet printer forms a layer of a hydrophilic composition on a surfaceof an intermediate transfer member using a liquid vehicle, such aswater, to apply a layer of the hydrophilic composition. The liquidvehicle is used as a mechanism to convey the hydrophilic composition toan image receiving surface to form a uniform layer of the hydrophiliccomposition on the image receiving surface.

Sacrificial Coating Composition

An embodiment of the present disclosure is directed to a sacrificialcoating composition formed on an intermediate transfer member of anindirect printing apparatus. The sacrificial coating composition is madefrom ingredients comprising at least one polymer selected from the groupconsisting of a hydrophilic polymer and a latex comprising polymerparticles dispersed in a continuous liquid phase. Additional ingredientscomprise at least one hygroscopic material; at least one oil-in-wateremulsion; and water. As will be discussed further below, theoil-in-water emulsion is prepared by emulsifying an oil with asurfactant and water. The oil-in-water emulsion is combined with thepolymer and other ingredients to produce the sacrificial coatingcomposition.

Hydrophilic Polymers

Hydrophilic polymers can act as a binder in the compositions of thepresent disclosure. In an embodiment, the hydrophilic polymers are watersoluble. For example, the hydrophilic polymers can be water soluble attemperatures below 100° C.

In an embodiment, the at least one hydrophilic polymer is selected fromthe group consisting of polyvinyl alcohol, a copolymer of vinyl alcoholand alkene monomers, poly(vinylpyrrolidinone) (PVP), poly(ethyleneoxide), hydroxyethyl cellulose, cellulose acetate, poly(ethyleneglycol), copolymers of poly(ethylene glycol), polyacrylamide (PAM),poly(N-isopropylacrylamide) (PNIPAM), poly(acrylic acid),polymethacrylate, acrylic polymers, maleic anhydride copolymers,sulfonated polyesters, polysaccharides, waxy maize starches and mixturesthereof. In an embodiment, the hydrophilic polymer is selected from waxymaize starches comprising more than 90 weight percent amylopectin, suchas 93 or 95 weight percent amylopectin or more, relative to the totalweight of the waxy maize.

In an embodiment, the at least one hydrophilic polymer is polyvinylalcohol. In an embodiment, the at least one polymer is a copolymer ofpolyvinyl alcohol and alkene monomers. Examples of suitable polyvinylalcohol copolymers include poly(vinyl alcohol-co-ethylene). In anembodiment, the poly(vinyl alcohol-co-ethylene) has an ethylene contentranging from about 5 mol % to about 30 mol %. Other examples ofpolyvinyl copolymer include poly(acrylic acid)-poly(vinyl alcohol)copolymer, polyvinyl alcohol-acrylic acid-methyl methacrylate copolymer,poly(vinyl alcohol-co-aspartic acid) copolymer etc.

It is well known that PVOH can be manufactured by hydrolysis ofpolyvinyl acetate to form, for example, partially hydrolyzed (87-89%),intermediate hydrolyzed (91-95%), fully hydrolyzed (98-98.8%) to superhydrolyzed (more than 99.3%) polyvinyl alcohol. In an embodiment, thepolyvinyl alcohol employed in the compositions of the present disclosurehas a hydrolysis degree ranging from about 75% to about 99.5% or 99.3%,such as about 80% to about 95%, or about 85% to about 90%.

The polyvinyl alcohol or copolymer thereof can have any suitablemolecular weight. In an embodiment, the weight average molecular weightranges from about 8000 to about 30,000 g-mole⁻¹, such as from about10,000 to about 25,000 g-mole⁻¹, or from about 13,000 to about 23,000g-mole⁻¹.

In an embodiment, the polyvinyl alcohol can provide a suitable viscosityfor forming a sacrificial coating on an intermediate transfer member.For example, at about 4% by weight polyvinyl alcohol in a solution of DIwater, at 20° C. the viscosity can range from about 2 cps to about 100cps, such as about 3 cps to about 15 or 30 cps, or about 3 cps to about5 cps, where the % by weight is relative to the total weight ofpolyvinyl alcohol and water.

Polyvinyl alcohol is a hydrophilic polymer and has good water retentionproperties. As a hydrophilic polymer, the coating film formed frompolyvinyl alcohol can exhibit good water retention properties, which canassist the ink spreading on the blanket. Because of its superiorstrength, the coatings formulated with polyvinyl alcohol can achieve asignificant reduction in total solid loading level. This may providesubstantial cost savings while providing a significant improvement ofthe coating film performance. In addition, the shelf life of PVOH basedformulations can be relatively long compared to some polymers, such asstarches. The mechanical properties of polyvinyl alcohol can besignificantly better when compared to starches.

The chemical structure of the hydrophilic polymer containing coating canbe tailored to fine-tune the wettability and release characteristics ofthe sacrificial coating from the underlying ITM surface. This can beaccomplished by employing one or more hygroscopic materials and one ormore surfactants in the coating composition.

Latex

The at least one polymer can be supplied in the form of a latexcomprising polymer particles dispersed in a continuous liquid phase. Thepolymer particles comprise one or more repeating polymeric units. In anembodiment, the polymeric units are selected from the group consistingof acrylic acid units, acrylate units, methacrylic acid units,methacrylate units, diene units, aliphatic nitrile units, vinyl etherunits, vinyl ester units, vinyl ketone units, vinylidene halide units,vinyl substituted heterocyclic amine units, acrylamide units,methacrylamide units, vinyl substituted aromatic hydrocarbon units,vinyl halide units and alkene units. In an embodiment, the polymerparticles comprise a polyvinyl acetate copolymer. In an embodiment, thelatex is an acrylic latex, such as a latex comprising one or moreacrylic resins made from at least one monomer selected from the groupconsisting of methyl acrylate, ethyl acrylate, butyl acrylate,methacrylic acid and acrylic acid. In an embodiment, the latex polymerparticles comprise one or more repeating polymeric units selected fromthe group consisting of n-butyl acrylate units, methacrylic acid units,methyl methacrylate units, styrene units and butadiene units. In anembodiment, the latex is a styrene/n-butyl acrylate/methacrylic acidterpolymer, examples of which are disclosed in co-pending U.S. patentapplication Ser. No. 14/288,633, filed on May 28, 2014, the disclosureof which is incorporated herein by reference in its entirety. Examplesof suitable latexes can include well known latexes such asStyrene/n-butyl acrylate latex, which has been commercially used, forexample, in aqueous overcoats in post finishing processes.

The monomers and amounts of monomers employed in the latex can beadjusted to provide desired properties for the transfix process. Forinstance, acrylic latex and/or styrene butadiene latex can be employedwith different methacrylic acid (MAA) loadings to alter the propertiesof the latex. In one example, different methacrylic acid loadings wereemployed for different styrene to n-butyl acrylate ratios to providevery different glass transition temperatures and softening points. Anexample of loading of methacrylic acid relative to styrene and n-butylacrylate in these latexes ranges from about 2 to about 20 wt %, such asabout 5 wt %, 10 wt % or 15 wt %, relative to the total weight of themethacrylic acid, styrene and n-butyl acrylate monomers.

The latexes can have any suitable solids content. Examples of suitablesolids content include ranges from about 5% to about 60% by weight, suchas about 10% to about 50% by weight, or about 20% to about 40% byweight, relative to the total weight of the liquid coating composition.

The latex polymer can have any suitable molecular weight. Examples ofsuitable weight average molecular weight, Mw, range from about 3000 toabout 300,000, such as about 5,000 to 100,000, or about 5,000 to about60,000. Examples of suitable number average molecular weight, Mn, rangefrom about 1,000 to about 30,000, such as about 2,000 to 20,000, orabout 5,000 to about 15,000.

Latex properties can be adjusted to provide any desired propertiessuitable for the aqueous transfix printing process. For example, the Tgof the latex can range from about −45° C. to about 100° C., such asabout −35° C. to 85° C., or about −25° C. to about 55° C. In an example,the viscosity of the latex is from about 3 cps to 800 cps at 25° C. Inan example, the pH of the latex ranges from about 1.5 to about 10, suchas about 3 to about 8. In an example, the softening point of the latexranges from about 100° C. to about 170° C.

In an example, the D50 particle size of the latex ranges from about 20to about 200 nm and the particle size distribution ranges from about 5nm to 300 nm, such as about 50 to about 250 nm. The gel content(insoluble portion in toluene) in the latex ranges, for example, from 0to about 20.0%.

The chemical structure of the latex containing coating can be tailoredto fine-tune the wettability and release characteristics of thesacrificial coating from the underlying ITM surface. This can beaccomplished by employing one or more hygroscopic materials and one ormore surfactants in the coating composition.

Hygroscopic Material

Any suitable hygroscopic material can be employed. The hygroscopicmaterial can be functionalized as a plasticizer. In an embodiment, theat least one hygroscopic material is selected from the group consistingof glycerol, sorbitol, glycols such as polyethylene glycol, vinylalcohols, xylitol, maltitol, polymeric polyols, glyceryl triacetate,glycouril, ionic liquids and mixtures thereof. A single hygroscopicmaterial can be used. Alternatively, multiple hygroscopic materials,such as two, three or more hygroscopic materials, can be used.

Oil-in-Water Emulsion

The addition of an oil-in-water emulsion to the undercoat formulationcan further improve the ink transfer efficiency during the transfixprocess. In an embodiment, the oil-in-water emulsion includes asurfactant. Any suitable oil and surfactant combination that willprovide the desired improvement in ink transfer efficiency can beemployed.

Examples of oils include silicone oils, perfluoroether oils, hydrocarbonoils and mixtures thereof. In an embodiment, the oil is mineral oilselected from the group consisting of paraffinic oils, naphthenic oils,aromatic oils and mixtures thereof. Oil viscosity can range, forexample, from about 10 cps to about 1000 cps, such as about 100 cps toabout 900 cps, or about 200 cps to about 800 cps. In an embodiment, theviscosity of silicone oil is less than 1000 centipoises.

Any suitable surfactants can be employed. In an embodiment, the at leastone surfactant is nonionic surfactant having a hydrophile lipophilebalance (“HLB”) value ranging from about 4 to about 15, such as, forexample about 8 to about 14. A single surfactant can be used.Alternatively, multiple surfactants, such as two, three or moresurfactants, can be used. For example, the surfactant can comprise amixture of a first surfactant and a second surfactant, the firstsurfactant having an HLB value ranging from about 8 or 10 to about 14 or15 and the second surfactant having an HLB value ranging from about 4 toabout 8 or 10, the first surfactant having a higher HLB value than thesecond surfactant.

In an embodiment, the surfactant can be a nonionic linear or branchedalcohol ethoxylate compound of general formula RO(CH₂CH₂O)_(x)H, where Ris an alkyl group ranging from C₆ to C₁₈ and x is a positive integerranging from 1 to 15. Other examples of suitable surfactants includepolyethylene glycol and polyethylene glycol trimethylnonyl ether.Examples of nonionic surfactants include secondary alcohol ethoxylatessuch as the Tergitol® 15-S series supplied by Dow Chemical Company. Inan embodiment, the surfactants are branched secondary alcoholethoxylates such as a branched secondary alcohol ethoxylate with 6 to 12moles of ethylene oxide (EO). Examples of suitable commerciallyavailable surfactants include the Tergitol® TMN series also supplied byDow Chemical Company, such as Tergitol TMN-6, a branched secondaryalcohol ethoxylate and Tergitol 15-s-7, a secondary alcohol ethoxylate.Formula 1 below is a general formula for the Tergitol series.Surfactants of formula 1 could have any suitable value for n, such as,for example, 1 to 15, or 6 to 12. For TMN-6 the valued of n is about 8.TMN-10 and TMN-100 are also potential candidates, which values for n ofabout 11 and 10, respectively.

In an embodiment, the cloud point for the alcohol ethoxylate is above30° C. Any other suitable surfactants can also be employed.

Additional Ingredients

The coating composition can optionally include one or more fillers oradditives. Fillers and additives can be selected to improve robustnessof the sacrificial coating, among other things. Examples of suitablefillers include metal oxide particles, such as colloidal silica ornano-aluminum oxide. Other optional additives include, for example,silicone, biocides and additional solvents and/or liquid carriers.Examples of biocides include ACTICIDES® CT, ACTICIDES® LA 1209 andACTICIDES® MBS from about 0.001 weight percent to about 0.2 weightpercent of the active ingredient. Examples of suitable liquid vehiclesinclude isopropanol and MEK (methyl ethyl ketone) or combinationsthereof in water.

Method of Making the Sacrificial Coating Composition

FIG. 1 illustrates a flow chart of a method of making an aqueousundercoat composition, according to an embodiment of the presentdisclosure. As shown at block 2 of FIG. 1, the method comprisesemulsifying an oil with surfactant to form an oil-in-water emulsion. Anysuitable method for forming a stable emulsion can be employed. Forexample, the mixing of the oil and surfactant can occur at asufficiently high shear for a suitable period of time to formmicro-sized or other suitably sized droplets of the oil dispersed in thesurfactant continuous phase. In an embodiment, the mixing of the oil andsurfactant occurs at a high shear speed of at least 6000 RPM, such as6500 RPM or 7000 RPM or more.

Improvements in transfer efficiency of the undercoat formulation areobserved when the oil-in-water emulsion is employed. The emulsificationand formulation process described herein produces a formulation which isstable towards phase separation over an extended time period, such as,for example, several days, a week or longer.

If the formulation is not stable towards phase-separation, little or noimprovements in transfer efficiency have been observed. Simple additionof oil to the original formulation does not result in a sufficientlystable formulation. If oil is added to the formulation directly, ratherthan as an emulsion, the oil phase separates from the aqueous solutionand will not be present in the intermediate thin film (skin) to aid withtransfer.

Any suitable amount of oil can be employed in the emulsion. For example,the oil can be loaded in the surfactant at a concentration ranging fromabout 0.1 wt % to about 15 wt % relative to the combined weight of theoil and surfactant, such as about 1 wt % to about 10 wt %, or about 3 wt% to about 5 wt %.

Referring to block 4 of FIG. 1, the method further comprises combiningingredients comprising (i) at least one polymer, (ii) at least onehygroscopic material, (iii) the oil-in water emulsion and (iv) water toproduce the sacrificial coating composition. The ingredients can becombined with the oil-in-water emulsion in any suitable order. In anembodiment, the at least one polymer, at least one hygroscopic material,and water are combined prior to addition of the oil-in-water emulsion.Alternatively, the at least one polymer and water are combined prior toaddition of the oil-in-water emulsion, which is added simultaneouslywith or prior to the at least one hygroscopic material.

Any of the polymers and hygroscopic materials described herein forforming the sacrificial layer can be employed. In an embodiment, any ofthe hydrophilic polymers described herein can be employed. In anembodiment, the at least one polymer is selected from the groupconsisting of polyvinyl alcohol (“PVA”) or a copolymer of vinyl alcoholand alkene monomers, as described in detail above.

Where the least one polymer is a hydrophilic polymer, the polymer can beheated sufficiently in water to dissolve the polymer. In an embodiment,the hydrophilic polymers are dissolved in water prior to mixing with theoil-in-water emulsion. For example, PVA and copolymers thereof taughtherein are often solid at room temperature, and can be dissolved in hotwater. In an embodiment, the other water soluble polymers taught hereincan also be dissolved in water at suitably high temperatures. Theheating can occur at any suitable temperature and for any suitableperiod of time sufficient to dissolve the polymer. In an embodiment, theheating can be carried out at a temperature of at least about 80° C.,such as about 85 to about 98° C., or about 90 to about 93° C. Forexample, the method can comprise heating polyvinyl alcohol to atemperature of at least about 80° C. for a time ranging from about 30minutes to about 90 minutes prior to combining ingredients to form thepolymer mixture.

In an embodiment, the at least one polymer can be in the form of a latexcomprising polymer particles dispersed in a continuous liquid phase. Anyof the latexes discussed herein can be employed. As described above, thepolymer particles can comprise one or more repeating polymeric unitsselected from the group consisting of acrylic acid units, acrylateunits, methacrylic acid units, methacrylate units, diene units,aliphatic nitrile units, vinyl ether units, vinyl ester units, vinylketone units, vinylidene halide units, vinyl substituted heterocyclicamine units, acrylamide units, methacrylamide units, vinyl substitutedaromatic hydrocarbon units, vinyl halide units and alkene units.

Any of the additional ingredients discussed herein can be employed. Forexample, the mixture can include one or more fillers, silicone,additional solvents, liquid carriers and biocides. These materials canbe mixed into the composition in any suitable manner.

The total amount of water in the wet composition prior to coating can beany suitable amount. In an embodiment where the hydrophilic polymers ofthe present application are employed, the total amount of water can be,for example, 60% by weight or more, such as from about 70 to about 97%by weight, or about 80 to about 95% by weight, relative to the totalweight of the composition. In an embodiment where a latex is employed,the total amount of water in the wet composition prior to coating canbe, for example, 30% by weight or more, such as from about 40 to about95% by weight, or about 45 to about 70% or 80% by weight, relative tothe total weight of the composition.

The ingredients can be mixed in any suitable amounts. For example, ifused, the hydrophilic polymer can be added in an amount of from about0.5 to about 30 weight percent, or from about 1 to about 10 weightpercent, or from about 1.5 to about 5 weight percent based upon thetotal weight of the coating mixture. If used, the latex can be added inan amount of from about 2 to about 50 weight percent, or from about 5 or10 to about 40 weight percent, or from about 25 to about 35 weightpercent based upon the total weight of the coating mixture. Thesurfactants can be present in an amount of from about 0.01 to about 4weight percent, or from about 0.1 to about 2 weight percent, or fromabout 0.2 to about 0.5 or 1 weight percent, based upon the total weightof the coating mixture. The hygroscopic material can be present in anamount of from about 0.5 to about 30 weight percent, or from about 2 toabout 25 weight percent, or from about 5 to about 20 weight percent,based upon the total weight of the coating mixture. In an embodiment,the amount of hydroscopic material present in a mixture with hydrophilicpolymers can be in an amount of from about 0.5 to about 15 weightpercent, or from about 2 to about 10 weight percent, or from about 3 toabout 8 weight percent, based upon the total weight of the coatingmixture. In an embodiment, the amount of hydroscopic material present ina mixture with latex polymers can be in an amount of from about 5 toabout 30 weight percent, or from about 10 or 15 to about 20 or 25 weightpercent, based upon the total weight of the coating mixture.

The compositions of the present disclosure can be used to form asacrificial coating over any suitable substrate. Any suitable coatingmethod can be employed, including, but not limited to, dip coating,spray coating, spin coating, flow coating, stamp printing, die extrusioncoatings, flexo and gravure coating and/or blade techniques. Inexemplary embodiments, suitable methods that can be employed to coat theliquid sacrificial coating composition on an intermediate transfermember include use of an anilox roller, as shown in FIG. 1, or an airatomization device such as an air brush or an automated air/liquidsprayer can be used for spray coating. In another example, aprogrammable dispenser can be used to apply the coating material toconduct a flow coating.

In an embodiment, the sacrificial coating composition is applied to theintermediate transfer member (“ITM”), where it is semi-dried or dried toform a film. The coating can have a higher surface energy and/or be morehydrophilic than the base ITM, which is usually a material with lowsurface free energy, such as, for example, a polysiloxane, such aspolydimethylsiloxane or other silicone rubber material, fluorosilicone,TEFLON, polyimide or combinations thereof.

In embodiments, the sacrificial coating can first be applied or disposedas a wet coating on an intermediate transfer member. An example of asuitable intermediate transfer member type printer and methods forapplying the sacrificial coating are disclosed in co-pendingapplications U.S. patent application Ser. No. 14/493,398 filed Sep. 23,2014 and U.S. patent application Ser. No. 14/493,474 filed Sep. 23,2014, the disclosures of which are incorporated herein by reference intheir entirety. A drying or curing process can then be employed. Inembodiments, the wet coating can be heated at an appropriate temperaturefor the drying and curing, depending on the material or process used.For example, the wet coating can be heated to a temperature ranging fromabout 30° C. to about 200° C. for about 0.01 to about 100 seconds orfrom about 0.1 second to about 60 seconds. In embodiments, after thedrying and curing process, the sacrificial coating can have a thicknessranging from about 0.02 micrometer to about 10 micrometers, or fromabout 0.02 micrometer to about 5 micrometers, or from about 0.05micrometer to about 1 micrometers.

In an embodiment, the sacrificial coating can cover a portion of a majorsurface of the intermediate transfer member. The major outer surface ofthe intermediate transfer member can comprise, for example, silicone ora fluorinated polymer.

It has been found that the sacrificial coating overcomes the wet imagequality problem discussed above by providing an ink wetting surface onthe intermediate transfer member. The coatings may also improve imagecohesion significantly to enable excellent image transfer.

EXAMPLES Example 1 Oil Emulsion Preparation

Five oil-in-water emulsions were prepared by loading a silicone oil,Wacker AK 500, available from Dow Corning and Wacker Chemie AG(viscosity 500 cps) silicone oil into TERGITOL TMN-6 surfactant. Theloading levels are 2.5%, 5%, 7.5%, 10% and 20%. The oil-surfactantmixture was mixed using a Polytron at speed of 7000 rpm at roomtemperature for 1 minute. Some oil loaded at 20% was separated fromsurfactant. All the other 4 mixtures were very stable over a few days.

Example 2 Undercoat Composition

Table 1 shows a formulation (composition 2A) prepared with polyvinylalcohol and oil emulsion and a formulation (composition 2B) preparedwith TMN-6 surfactant without oil. The oil emulsion of composition 2Awas prepared with 10% AK500 silicone oil and 90% TERGITOL TMN-6surfactant. All these solutions are very stable.

TABLE 1 PVOH-oil emulsion vs. TMN-6 only Emulsion of Tergitol TMN-6/AK500 oil Surfactant Compo- (ratio = TMN-6 DI sition PVOH 90:10) (%)Loading Glycerol Water Total 2A 1.50% 0.25% — 5.0% 93.25% 100.00% 2B1.50% — 0.25% 5.0% 93.25% 100.00%

Example 3 Coating Process

The undercoat compositions 2A and 2B were coated on a blanket substrateusing a Pamarco anilox roll 165Q13 by hand. The blanket substratesurface was coated with a film comprising a fluorinated polymer (DAI-EL™G-621 manufactured by Daikin Industries, Ltd.) and AO700 (anaminoethyl-aminopropyl trimethoxysilane crosslinker from Gelest). Thehotplate was setup at 60° C. while the blanket substrate temperature wasaround 50° C. The sacrificial coating wet film thickness was around 4-5microns and the dry film thickness was around 500 nm to 1.5 microns. Thecoated film was dried in oven at 60° C. for 30 seconds.

Example 4 Optical Microscope Images—Film Forming Property Evaluation

In order to make ink having good wetting and spreading on the undercoatfilm, it is desirable to achieve a continuous uniform film with theundercoat solution. To determine whether continuous uniform films wereformed, optical microscope images were taken of the films formed inExample 3. These images are shown in FIG. 2.

Both Composition 2A and Composition 2B formed a continuous film, butwith some defects on the surface. There are defects in both of theformulations, so these defects may be due to the fluorosilicone blanket,which was hand coated in the lab.

Example 5 Air Brush Transfer Test

A transfer test of the films of Example 3 was carried out using Collinink PWK -1223. The ink was sprayed on the blankets coated with the driedfilms of Example 3 by air brush. The transfer condition was 320° F., 50psi and 5 seconds dwell time. The ink was transferred from the blanketsto 120 gsm Digital Color Elite Gloss paper.

The images of FIG. 3 show the transfer results for the film ofcomposition 2A (made with oil emulsion) vs. the film of composition 2B(made with TMN-6 surfactant only (no oil)) at different transfertemperatures. The top image is the blanket after transfer and the bottomimage is the DCEG paper after ink was transferred. The ink tested herecan only be transferred at around 120° C. for undercoat without loadingof oil emulsion. Much less residual ink remains on the blanket forformulations with the oil emulsion at lower transfer temperatures. Thetransfer temperature can be dropped around 20° C. for formulation withoil emulsion (from 120° C. to 100° C.). The darker the DCEG paper, thebetter the ink transferred. These results show that the film made withthe oil emulsion resulted in a reduction in transfer temperature andimproved release properties.

Example 6 Undercoat Compositions

Example 6: Sacrificial coating compositions were prepared with Xeroxexperimental latex-L, a styrene/n-butyl acrylate/methacrylic acidterpolymer with a relatively low Tg of about 52° C. to about 53 oC, orXerox experimental latex-H, a styrene/n-butyl acrylate/methacrylic acidterpolymer with a relatively high Tg of about 80° C. to about 82° C. Thecomponents for these example latexes are shown in more detail in Table 2below. The oil-in-water emulsions of examples 6-1, 6-2 and 6-3 wereprepared with 10% AK500 silicone oil and 90% Tergitol TMN-6 surfactant.All these solutions were very stable.

TABLE 2 Latex Type XRCC XRCC Latex-L Latex-H Styrene (%) 54 67.9 nBA (%)34 18.6 Methacrylic acid (%) 12 13.5 bCEA (pph on St + nBA + MAA) 3 3ADOD (pph on St + nBA + MAA) 0.35 0.35 DDT#1 (pph on total St + nBA +MAA) 0.62 0.26 DDT#2 (pph on total St + nBA + MAA) 2.44 2.13 Dowfax (pphon St + nBA + MAA) 1 1 APS (pph on St + nBA + MAA) 1.5 1.5 Dowfaxpartition 15/85 15/85 Seed % 1 1 Particle Size D50 (nm) 100.3 120.1Particle Size D95 (nm) 141.1 172.4 Zeta Potential (mV) ± STD −64.5 ±15.0 −63.6 ± 10.2 Conductivity (mS/cm) 0.129 0.074 pH 1.8 1.83 Solids(%) 39.9 41.9 Mw (k) 43.2 47.4 Mn (k) 12.4 13.6 PDI (polydispersity) 3.53.5 Tg (° C.) - onset 62.9 81.8 Acid Value (titration) 95.1 50.7 Styrene(ppm) in latex 56 98 nBA (ppm) in latex 884 14 MAA (ppm) in latex 51 149% Gel Content 3.8 13.4 Ts (softening point ° C.) 142.3 161.9

Example 6-1: A sacrificial coating solution was prepared by combiningand mixing 31.25 g Xerox experimental latex-L and 18.75 g glycerol into49.75 g DI water. Next, 0.25 g oil-in-water emulsion was added into themixture to make it 100 g of solution.

Example 6-1A: A sacrificial coating solution was prepared by combiningand mixing 31.25 g Xerox experimental latex-L and 18.75 g glycerol into49.75 g DI water. Next, 0.25 g TMN-6 surfactant was added into themixture to make it 100 g of solution.

Example 6-2: A sacrificial coating solution was prepared by combiningand mixing 31.25 g Xerox experimental latex-L and 18.75 g sorbitol into49.75 g DI water. Next, 0.25 g oil-in-water emulsion was added into themixture to make it 100 g of solution.

Example 6-2A: A sacrificial coating solution was prepared by combiningand mixing 31.25 g Xerox experimental latex-L and 18.75 g sorbitol into49.75 g DI water. Next, 0.25 g Tergitol TMN-6 surfactant was added intothe mixture to make it 100 g of solution.

Example 6-3: A sacrificial coating solution was prepared by combiningand mixing 31.25 g Xerox experimental latex-H and 18.75 g sorbitol into49.75 g DI water. Next, 0.25 g oil-in-water emulsion was added into themixture to make it 100 g of solution.

Example 6-3A: A sacrificial coating solution was prepared by combiningand mixing 31.25 g Xerox experimental latex-H and 18.75 g sorbitol into49.75 g DI water. Next, 0.25 g Tergitol TMN-6 surfactant was added intothe mixture to make it 100 g of solution.

Example 7 Undercoat Compositions

Example 7: Sacrificial coating compositions were prepared withcommercially available BASF acrylic latexes included Joncryl® 74-A,which is a soft film forming acrylic emulsion that provides filmformation and excellent rub, water, and grease resistance to ink,overprint varnish, and functional packaging. Joncryl® 77 is a hard filmforming acrylic latex which provides film formation and printability toink and overprint varnish formulations. The oil-in-water emulsions ofExamples 7-1 and 7-2 were prepared with 10% AK500 silicone oil and 90%Tergitol TMN-6 surfactant. All these solutions were very stable. Coatingsolutions were prepared as follows:

Example 7-1: A sacrificial coating solution was prepared by combiningand mixing 31.25 g BASF Joncryl 74A latex and 18.75 g sorbitol into49.75 g DI water. Next, 0.25 g oil-in-water emulsion was added into themixture to make it 100 g of solution.

Example 7-1A: A sacrificial coating solution was prepared by combiningand mixing 31.25 g BASF Joncryl 74A latex and 18.75 g sorbitol into49.75 g DI water. Next, 0.25 g TMN-6 surfactant was added into themixture to make it 100 g of solution.

Example 7-2: A sacrificial coating solution was prepared by combiningand mixing 31.25 g BASF Joncryl 77 latex and 18.75 g sorbitol into 49.75g DI water. Next, 0.25 g oil-in-water emulsion was added into themixture to make it 100 g of solution.

Example 7-2A: A sacrificial coating solution was prepared by combiningand mixing 31.25 g BASF Joncryl 77 latex and 18.75 g sorbitol into 49.75g DI water. Next, 0.25 g TMN-6 was added into the mixture to make it 100g of solution.

Example 8 Undercoat Composition

The formulations of Table 2 were prepared with Celanese latexes andeither an oil-in-water emulsion or a TMN-6 surfactant (no oil,surfactant only). The formulations of Example 8-1 and ComparativeExample 8-1A included RESYN 2920, which is an emulsion comprising anorganic acrylic polymer and inorganic silica. The two phases of thisemulsion are chemically linked to insure homogeneous distribution. Theformulations of Examples 8-2 and 8-3 and Comparative Examples 8-2A and8-3A included Dur-O-Cryl 69A, which is a water-based acrylic polymerwith self-crosslinking functionality. The oil-in-water emulsions wereall prepared with 10% AK500 silicone oil and 90% Tergitol TMN-6surfactant. All these solutions were very stable.

Example 8-1: A sacrificial coating solution was prepared by combiningand mixing 31.25 g Celanese Resyn 2920 latex and 18.75 g glycerol into49.75 g DI water. Next, 0.25 g oil-in-water emulsion was added into themixture to make it 100 g of solution.

Example 8-1A: A sacrificial coating solution was prepared by combiningand mixing 31.25 g Celanese Resyn 2920 latex and 18.75 g glycerol into49.75 g DI water. Next, 0.25 g Tergitol TMN-6 surfactant was added intothe mixture to make it 100 g of solution.

Example 8-2: A sacrificial coating solution was prepared by combiningand mixing 31.25 g Celanese Dur-O-Cryl latex and 18.75 g glycerol into49.75 g DI water. Next, 0.25 g oil-in-water emulsion was added into themixture to make it 100 g of solution.

Example 8-2A: A sacrificial coating solution was prepared by combiningand mixing 31.25 g Celanese Dur-O-Cryl latex and 18.75 g glycerol into49.75 g DI water. Next, 0.25 g Tergitol TMN-6 surfactant was added intothe mixture to make it 100 g of solution.

Example 8-3: A sacrificial coating solution was prepared by combiningand mixing 31.25 g Celanese Dur-O-Cryl 69A latex and 18.75 g sorbitolinto 49.75 g DI water. Next, 0.25 g oil-in-water emulsion was added intothe mixture to make it 100 g of solution.

Example 8-3A: A sacrificial coating solution was prepared by combiningand mixing 31.25 g Celanese Dur-O-Cryl 69A latex and 18.75 g sorbitolinto 49.75 g DI water. Next, 0.25 g Tergitol TMN-6 surfactant was addedinto the mixture to make it 100 g of solution.

Example 9 Coating Process

Each of the undercoat solutions of Examples 6, 7 and 8 were coated onblanket substrate using anilox roll 165Q13 by hand. The substrate wasmade from fluorinated polymer G621 with AO700 as a crosslinker. Thehotplate was setup at 60° C. while the substrate temperature was around50° C. The wet film thickness was around 4-5 microns and the dry filmthickness was around 500 nm to 1.5 microns. The coated film was dried inoven at 60° C. for 30 seconds.

Example 10 Optical Microscope Images—Film Forming Property Evaluation

In order to make ink having good wetting and spreading on the undercoatfilms, it is desirable to achieve a continuous uniform film withundercoat solution. FIGS. 4, 5 and 6 show optical microscope imagestaken of films made from the compositions of Examples 6, 7 and 8, whichwere coated on G621 blanket substrates.

Example 6-1 and Example 6-2 were prepared using Xerox experimentallatex-L but different humectants. Example 6-1 was loaded with 18.75%glycerol; Example 6-2 was loaded with 18.75% sorbitol. Both formulationsform a nice continuous uniform film, as shown by the optical microscopeimages of FIG. 4.

Example 6-3 was prepared using Xerox experimental-H latex. Example 7-1was prepared using BASF Joncryl 74A latex. Both formulation use the samehumectant (sorbitol). Formulation using Xerox experimental latex-Hgenerates a continuous and more uniform coating film, as shown by theoptical microscope images of FIG. 5.

Examples 8-1 and 8-2 were prepared using the same humectant (glycerol)but different latexes from Celanese. A Resyn 2920 latex was used in theExample 8-1 formulation; Dur-O-Cryl 69A was used in the Example 8-2formulation. The surface uniformity for both formulations was verysimilar, as shown by the optical microscope images of FIG. 6.

Example 11 Air Brush Transfer Test

Collin ink PWK -1223 was used for transfer test. The ink was sprayed onthe coated blanket by air brush. The transfer condition was 320° F., 50psi and 5 seconds dwell time. The ink was transferred from blanket to120 gsm Digital Color Elite Gloss paper.

The images of FIG. 7 show the transfer results of the coatings ofExamples 6-1A and 6-2A (with no oil-in-water emulsion) vs. Examples 6-1and 6-2 (with oil-in-water emulsion). The Example 6-1 and 6-1A are theresults shown in the top row and Example 6-2 and 6-2A are the resultsshown in the bottom row. The top image in each row is the blanket aftertransfer and the bottom image is the DCEG paper after ink transfer.There is much less residual ink on the blanket coated with anoil-in-water emulsion solution. There are some residual ink on theblanket coated with no oil-in-water emulsions (Examples 6-1A and 6-2A,in column labeled “without oil”). The darker the DCEG paper, the betterthe ink transferred.

The group images of FIG. 8 show the transfer test results for two setsof formulations, the first made with BASF latex Joncryl 74A loaded withsorbitol (Examples 7-1 and 7-1A in the top row) and the second made withCelanese latex Resyn 2920 loaded with glycerol (Examples 8-1 and 8-1A inthe bottom row). The top image is the blanket after transfer and thebottom image is the DCEG paper after ink transfer. There is a lot ofresidual ink on blanket for the formulations without oil emulsion(Examples 7-1A and 8-1A, in column labeled “without oil”). The inktransfer was dramatically improved after loading with the oil emulsion.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the disclosure are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements. Moreover, all ranges disclosed hereinare to be understood to encompass any and all sub-ranges subsumedtherein.

While the present teachings have been illustrated with respect to one ormore implementations, alterations and/or modifications can be made tothe illustrated examples without departing from the spirit and scope ofthe appended claims. In addition, while a particular feature of thepresent teachings may have been disclosed with respect to only one ofseveral implementations, such feature may be combined with one or moreother features of the other implementations as may be desired andadvantageous for any given or particular function. Furthermore, to theextent that the terms “including,” “includes,” “having,” “has,” “with,”or variants thereof are used in either the detailed description and theclaims, such terms are intended to be inclusive in a manner similar tothe term “comprising.” Further, in the discussion and claims herein, theterm “about” indicates that the value listed may be somewhat altered, aslong as the alteration does not result in nonconformance of the processor structure to the illustrated embodiment. Finally, “exemplary”indicates the description is used as an example, rather than implyingthat it is an ideal.

It will be appreciated that variants of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be combined intomany other different systems or applications. Various presentlyunforeseen or unanticipated alternatives, modifications, variations, orimprovements therein may be subsequently made by those skilled in theart which are also intended to be encompasses by the following claims.

What is claimed is:
 1. An method of making a sacrificial coatingcomposition, the method comprising: emulsifying an oil with surfactantand water to form an oil-in-water emulsion; combining ingredientscomprising (i) at least one polymer, (ii) at least one hygroscopicmaterial, (iii) the oil-in water emulsion and (iv) water to produce thesacrificial coating composition, wherein the at least one polymer is alatex comprising polymer particles dispersed in a continuous liquidphase.
 2. The method of claim 1, wherein combining ingredients comprisesmixing the at least one polymer, the at least one hygroscopic materialand water to form a polymer mixture and then combining the polymermixture and the oil-in-water emulsion.
 3. The method of claim 1, whereinthe emulsifying comprises mixing the oil and surfactant at a high shearspeed of at least 6000 RPM.
 4. The method of claim 1, wherein prior tomixing the oil and surfactant, the oil is loaded in the surfactant at aconcentration ranging from about 0.1 wt % to about 15 wt %, relative tothe combined weight of the oil and surfactant.
 5. The method of claim 1,wherein the polymer particles comprise one or more repeating polymericunits selected from the group consisting of acrylic acid units, acrylateunits, methacrylic acid units, methacrylate units, diene units,aliphatic nitrile units, vinyl ether units, vinyl ester units, vinylketone units, vinylidene halide units, vinyl substituted heterocyclicamine units, acrylamide units, methacrylamide units, vinyl substitutedaromatic hydrocarbon units, vinyl halide units and alkene units.
 6. Themethod of claim 1, wherein the wherein the latex has a glass transitiontemperature of ranging from about −45° C. to about 100° C., a weightaverage molecular weight ranging from about 3000 to about 300,000, and aparticle size ranging from 50 nm to 300 nm.
 7. The method of claim 1,wherein the latex has a viscosity of about 3 cps to about 800 cps at 25°C., a pH ranging from about 1.5 to about 10, and a solid content rangingfrom 5% to about 60%.
 8. The method of claim 1, wherein the polymerparticles comprise a styrene/n-butyl acrylate/methacrylic acidterpolymer.
 9. The method of claim 1, wherein the at least onehygroscopic material is selected from the group consisting of glycerol,sorbitol, glycols,vinyl alcohols, xylitol, maltitol, polymeric polyols,glyceryl triacetate, glycouril, ionic liquids and mixtures thereof. 10.The method of claim 1, wherein the oil is selected from the groupconsisting of a silicone oil, a perfluoroether oil and a hydrocarbon oiland mixtures thereof.
 11. The method of claim 1, wherein the surfactantis a nonionic surfactant with hydrophile lipophile balance (HLB) valueof from 4 to15.
 12. The method of claim 1, wherein the surfactant is asecondary alcohol ethoxylate.
 13. The method of claim 1, wherein thesurfactant is a branched secondary alcohol ethoxylate with 6 to 12 molesof ethylene oxide (EO).
 14. The method of claim 1, wherein thesurfactant comprises a mixture of a first surfactant and a secondsurfactant, the first surfactant having a hydrophile lipophile balance(“HLB”) value ranging from about 8 to about 15 and the second surfactanthaving an HLB value ranging from about 4 to about 10, the HLB value forthe first surfactant being higher that the HLB value for the secondsurfactant.
 15. The method of claim 1, wherein the at least one polymerfurther comprises a hydrophilic polymer.
 16. The method of claim 15,wherein the hydrophilic polymer is selected from the group consisting ofpolyvinyl alcohol, a copolymer of vinyl alcohol and alkene monomers,poly(vinylpyrrolidinone) (“PVP”), poly(ethylene oxide), hydroxyethylcellulose, cellulose acetate, poly(ethylene glycol), copolymers ofpoly(ethylene glycol), polyacrylamide (PAM), poly(N-isopropylacrylamide)(“PNIPAM”), poly(acrylic acid), polymethacrylate, acrylic polymers,maleic anhydride copolymers, sulfonated polyesters, polysaccharides,waxy maize starches and mixtures thereof.
 17. The method of claim 15,wherein the at least one hydrophilic polymer is waxy maize starch. 18.The method of claim 17, wherein the waxy maize starch comprises morethan 90 weight percent amylopectin.
 19. A method of making a sacrificialcoating composition, the method comprising: emulsifying an oil withsurfactant and water to form an oil-in-water emulsion, the oil beingselected from the group consisting of a silicone oil, a perfluoroetheroil and mixtures thereof and the surfactant comprising a branchedsecondary alcohol ethoxylate with 6 to 12 moles of ethylene oxide (EO);combining ingredients comprising (i) at least one polymer, (ii) at leastone hygroscopic material, (iii) the oil-in-water emulsion and (iv) waterto produce the sacrificial coating composition, wherein the at least onepolymer is selected from the group consisting of a hydrophilic polymer,a latex comprising polymer particles dispersed in a continuous liquidphase, or mixtures thereof, and wherein the at least one hydrophilicpolymer is selected from the group consisting of polyvinyl alcohol, acopolymer of vinyl alcohol and alkene monomers, poly(vinylpyrrolidinone)(“PVP”), poly(ethylene oxide), hydroxyethyl cellulose, celluloseacetate, poly(ethylene glycol), polyacrylamide (PAM),poly(N-isopropylacrylamide) (“PNIPAM”), poly(acrylic acid),polymethacrylate, acrylic polymers, maleic anhydride copolymers,sulfonated polyesters, waxy maize starches and mixtures thereof.